This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Multiple-stage ion-trap mass spectrometric approaches for characterizing monoacyl-PIM (triacylated PIM) and diacyl-PIM (tetracylated PIM) have been developed (14). Identification of the fatty acid substituents and their positions on the glycerol backbone can be achieved as described above.